Hepatitis B, which is usually caused by transfusing blood of HBV positive patient or others, is hardly remedied, and there is no drug suitable for complete remedy thereof. Most suitable prophylaxis is a vaccine consisting of HBV surface antigen (hereinafter, referred to as "HBs antigen", "HBsAg" or "s antigen"). However, it is very difficult to produce the HBsAg vaccine on an industrial scale, because HBV is infectious only to human subjects and chimpanzee (it has never been successful to make a cell culture infected with HBV), and owing to this specificity of HBV, HBsAg must be obtained only from human blood serum.
It has recently been proposed to prepare HBsAg by E. coli with recombinant DNA instead of using human blood serum (cf. Japanese Patent Laid Open Application No. 104887/1980). However, according to this method using E. coli, it is still difficult to produce the desired HBsAg on an industrial scale, because the produced HBsAg is easily decomposed within the cells of E. coli and further growth of E. coli is inhibited by the produced HBsAg, which results in less productivity of HBsAg.
It has also been proposed to transform a certain animal cells with a cloned DNA (cf. Japanese Patent Laid Open Application No. 39784/1982). However, the recombinant DNA used in this method is prepared by inserting HBV DNA into E. coli plasmid pBR322, said plasmid pBR322 being not subjected to deletion of the site of inhibiting replication in mammalian cells and to insertion of a DNA (e.g. SV40 DNA) which can replicate in mammalian cells, and hence, when this recombinant DNA is introduced into mammalian cells, for instance monkey cells (e.g. COS Cells, cf. Gluzman, Y.; Cell, 23, 175-182, 1981), it can not effectively be grown in the cells, and further there is produced only HBs antigen with avoiding the production of HBe antigen.
It is also known to use SV40 DNA as a vector for preparing a recombinant DNA wherein a rabbit .beta.-globulin gene is inserted (cf. Y. Takagi, et al, "Procedure for Experiment in Genetic Engineering", Third Ed., published by Kodansha, July 1, 1981, pages 122-125), but in this method, the SV40 DNA is a long fragment containing also the promoter region and the resultant recombinant DNA is directly inserted into mammalian cells which are infected thereby together with a helper SV40 mutant DNA to produce viral particles.
Furthermore, it is known that HVB proteins are produced by a recombinant DNA comprising an HBV fragment recombined with SV40 DNA vector (cf. Japanese Patent Laid Open Application No. 56685/1983=U.S. Ser. No. 298,235 and Japanese Patent Laid Open Application No. 995/1983=U.S. Ser. No. 249,352). However, in these invention, the SV40 DNA vector is a long fragment containing also the promoter region like above and the produced proteins comprise mainly HBs antigen, and it can not produce the protein on a large scale.